Issues with array_push

I have a controller in which I want to set up a log where a specific user can see a mission's history (something that would look like ( {user} set the mission as {mission status}, whether he accepts a mission or not. I would like to set this "status" inside an array so when I make it show up, it would look like a list of the events.

So far, here's how it looks:

/**
 * @Route("/accept/{id}", name="mission_accept")
 * @Method("POST")
 */
public function acceptAction(Request $request, Mission $mission){
    $form = $this->acceptMission($mission);
    $form->handleRequest($request);
    if($form->isSubmitted() && $form->isValid()){
        $user = $this->container->get('security.token_storage')->getToken()->getUser();
        $em = $this->getDoctrine()->getManager();
        $mission->setStatut("filled");
        $mission->setAppliedSchool($user->getEcole());
        $history = $mission->getHistory();
        $mission->setHistorique(array_push($history, 'Mission '.$mission->getStatut().' by'. $mission->getAppliedSchool()));
        $em->persist($mission);
        $em->flush();
    }
    return $this->redirectToRoute('mission_index');
}

"getAppliedSchool" gets the user that has changed the mission's status by something else by accepting or declining the mission.

My issue is that when I try to save this status, everything works fine except for the array, where I go from the default value in the database ( a:0:{}) to something like this: a:2, and I don't know why. I think I'm doing something wrong but I can't tell where and how.

Any idea ?

The thing is that array_push doesn't return an array. So just change your code a bit:

array_push($history, 'Mission '.$mission->getStatut().' by'. $mission->getAppliedSchool());
$mission->setHistorique($history);